This invention relates to an all-organic corrosion inhibiting composition comprising (a) 6,6xe2x80x2,6xe2x80x3-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid; and (b) a water-soluble phosphonated oligomer salt. The invention also relates to a process for inhibiting corrosion in a closed recirculating cooling water system.
Chemicals are added to recirculating closed and semi-closed cooling water systems, e.g. hot water boilers, chilled water systems, sweet water, free cooling tempered water, process condensate waer, desalter water, geothermal brine, lithium bromide refrigerant brines, automotive engine coolant jacket systems, water pumps and engine jackets, etc. to prevent the corrosion of metal surfaces, particularly corrosion of steel, brass, aluminum, and copper, that are in contact with water. A closed system recirculates water without evaporative cooling and usually has a low level of water loss.
For years, inorganic chemicals, such as heavy metals (chromate and molybdate) or nitrite containing corrosion inhibitors, were typically used in closed systems. When chromate was banned from use in many recirculating cooling water systems and regulations were enacted restricting the discharge of other inorganic chemicals, interest developed in using corrosion inhibitor formulations containing only organic chemicals for closed cooling water systems.
One of the widely used closed system organic corrosion inhibitors is 6,6,6-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid which is available from FMC Corporation under the trademark xe2x80x9cBELCOR 590xe2x80x9d. BELCOR 590 is a 49% solids wet cake of 6,6,6-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid. It is known to use BELCOR 590 as a corrosion inhibitor in formulations for closed recirculating cooling water systems.
U.S. Pat. No. 5,386,038 discloses that a mixture of water-soluble phosphonated oligomer salts is effective as corrosion inhibitors in formulations for both open and closed recirculating cooling water systems. BRICORR 288, available from Albright and Wilson, is a 40% solids mixture of water-soluble phosphonated oligomer salts.
Although many organic formulations were developed to inhibit the corrosion of metals in recirculating cooling water systems, these formulations were more expensive than the inorganic formulations they replaced. In order to make these all-organic formulations cost competitive, formulators search for blends which are synergistic. Organic synergistic blends can compete with inorganic corrosion inhibitors because they are effective at significantly lower dosages. The prior art does not disclose blends of 6,6,6-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid and water soluble phosphonated oligomer salts to inhibit the corrosion of metal exposed to closed recirculating aqueous systems.
This invention relates to all-organic corrosion inhibiting compositions comprising:
(a) 6,6xe2x80x2,6xe2x80x3-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid; and
(b) water-soluble phosphonated oligomer salts.
The invention also relates to a process for inhibiting corrosion in a closed recirculating cooling water system. The corrosion inhibiting compositions are particularly effective at inhibiting the corrosion of metal surfaces made of mild steel where steel is found alone in the components of the cooling system, or where there are components present made of other metals, such as brass, copper, aluminum, and or alloys. The blends are synergistic because they inhibit corrosion to a greater extent than was expected in view of the corrosion inhibition activity of the individual components. Because the blends exhibit synergism, they are more cost effective. The compositions are environmentally desirable because they are relatively non-toxic, contain no heavy metals, and have low or no phosphorus. The compositions may also contain an azole compound and/or a water-soluble, anionic polymeric dispersant, silicates, and other components known in the art for use in corrosion inhibiting compositions.
Component (a) of the corrosion inhibitor composition is 6,6xe2x80x2, 6xe2x80x3-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid. A commercially available product containing this component is BELCOR 590 sold by FMC as a 49% solids wet cake.
Component (b) of the corrosion inhibitor composition is a water-soluble phosphonated oligomer salt, preferably a sodium salt, and typically found as a mixture of oligomers. These oligomers are described in U.S. Pat. No. 5,386,038 which is incorporated by reference. The general structural formula for these water-soluble phosphonated oligomer salts is:
H[CHRCHR]nxe2x80x94PO3M2
wherein at least one R group in each unit is a COOM, CH2OH, phosphono, sulphono, or sulphato group. The other R group, which may be the same as or different from the first R group, is hydrogen or a COOM, hydroxyl, phosphono, sulphono, sulphato, C1-7alkyl, carboxylate, hydroxyl C1-7alkyl, or a C1-7alkenyl group. M is a cation such that the phosphonated oligomer is water soluble and n is 1 to 6, preferably  greater than 1 and  less than 6.
Preferably used as the water-soluble phosphonated oligomer salt are salts having the following specific version of the above general structural formula:
H[CH(CO2Na)xe2x80x94CH(CO2Na)]nPO3Na2 where xe2x80x9cnxe2x80x9d  less than 5.
The weight ratio of active 6,6,6-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid to active phosphonated oligomer is from 9:1 to 1:9, preferably from 4:1 to 1:1. It has been found that a synergy exists between the 6,6,6-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid and the water-soluble phosphonated oligomer salts if used in these amounts in a closed recirculating cooling water system.
Azoles can also be used in the corrosion inhibiting compositions to improve corrosion inhibition for copper and copper alloys. Examples of azoles that can be used in the corrosion inhibiting compositions include thiazoles and triazoles, for instance mercaptobenzothiazole, tolyltriazole, benzotriazole and 5-methylbenzotriazole. Active azole levels in the corrosion inhibitor systems range from 0.1 to 15 parts, preferably from 2 to 3 parts by weight of azole, based upon the total weight of the composition.
It may also be useful to use water soluble, low molecular weight, anionic polymeric dispersants when treating waters that contain high levels of impurities such as hardness salts (calcium carbonate, calcium phosphate) or suspended solids (iron or corrosion products). Examples of water soluble, low molecular weight, anionic polymeric dispersants that can be used in the corrosion inhibiting compositions include, but are not limited to, polyacrylates, acrylic acid copolymers, polymethacrylates, polymaleic anhydrides, maleic anhydride copolymers and sulfonated polymers and copolymers with molecular weights typically ranging from 500 to 20,000. These water soluble, low molecular weight, anionic polymeric dispersants exhibit deposit control efficacy using general dispersancy for suspended solids and corrosion products as well as sequestration, crystal lattice distortion and threshold inhibition for mineral scale deposits. The addition of a polymeric dispersant to the formulation is optional and may be unnecessary in waters with low levels of impurities. The water-soluble, low molecular weight, anionic polymeric dispersants are used in the corrosion inhibitor systems in the amount of 0.1 to 5 parts, preferably from 0.4 to 0.6 parts by weight of polymer, based upon the total weight of the composition.
A preferred closed recirculating cooling water corrosion inhibitor formulation of the present invention includes BELCOR 590 and BRICORR 288 at an actives ratio from 1:9 to 9:1 with total active BELCOR 590/BRICORR 288 solids in the formulation ranging from 1 to 25 parts, an azole compound with total active solids in the formulation ranging from 0.1 to 15 parts and a water soluble, a low molecular weight, anionic polymeric dispersant for mineral scale, and corrosion products dispersancy with total active solids in the formulation ranging from 0.1 to 5 parts, by weight based upon the total weight of the composition. These formulations are used in amounts of 100 to 10,000 ppm as product in cooling water systems, preferably in amounts of 500 to 5000 ppm.
A particularly preferred closed recirculating cooling water corrosion inhibitor composition is a blend of BELCOR 590 and BRICORR 288 at an actives ratio of 2:1 with total active BELCOR 590/BRICORR 288 solids of 5 to 6 parts, tolyltriazole at 2 to 3 parts and a water soluble, low molecular weight, anionic polymeric dispersant at 0.4 to 0.6 parts, by weight based upon the total weight of the composition. Preferably, the composition is used in amount of 1000 to 2000 ppm as product in cooling water systems.
The components of the corrosion inhibitor are typically formulated by mixing them in the following sequence: water, Belcor 590, BRICORR 288, azole, water soluble, low molecular weight, anionic polymeric dispersant. Sodium hydroxide can also be added to improve stability by elevating pH.
The following are the abbreviations used in the examples:
BELCOR is BELCOR 590 is a 49% solids wet cake of 6, 6xe2x80x2, 6xe2x80x3-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid, manufactured by FMC.
BRICORR is BRICORR 288, a 40% solids aqueous mixture of water-soluble phosphonated oligomer salts, manufactured by Albright and Wilson Inc.
MPY corrosion rate in xe2x80x9cMils Per Yearxe2x80x9d or 0.001 inches per year.